I meant I'm shamelessly promoting it, but here's how it works essentially...

It's a multi OS daemon/service that synchronizes between devices using encrypted transmission. You can have 2 way sync or 1 way sync... there are many ways to customize it; for example I write using Obsidian which uses normal flat text files and a directory structure for everything so I sync that folder to whatever devices (grapheneos phone, Linux box, grapheneos tablet in my specific case) and then point Obsidian to that folder on each device and boom it works. As soon as I've written it's synchronized. I'm also using it for BTC Wallet backups on my phone; I'm backing up my BTC wallet, putting that in a folder that syncs and it's sent to my Linux box which has a copy and then also runs a nightly backup of its own. You can tell it not to sync on cellular and even to only sync on specific wifinif you need to. I do the same for my phone photos, and when I edit them on Linux then sync thing knows and syncs the edits back to my phone - no Appl$ or Googl$ clouds involved. 💘

PS sorry this ended up like a novel but it's a multi faceted app.